The water industry is facing many challenges, one of which is the understanding and control of disinfection by-products (DBPs). The negative effects of DBPs on public health and the environment have raised concern over the use of these compounds; the presence of these compounds in a water supply is now strictly regulated in many countries. The DBPs have been found to be carcinogenic, mutagenic, hepatoxic and to cause adverse reproductive and developmental effects in human beings.
Haloacetic acids (HAAs) are one of the main DPBs that have been identified in chlorinated water. HAAs are considered to be hazardous to humans at high concentrations and prolonged exposure, and maximum regulatory limits for HAAs have been established in a number of industrialized countries. The primary HAAs formed during chlorination are monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), monobromoacetic acid (MBAA), dibromoacetic acid (DBAA), tribromoacetic acid (TBAA), bromochloroacetic acid (BCAA), chlorodibromoacetic acid (CDBA) and bromodichloroacetic acid (BDCAA). The first five of these are the most common, and are regulated under the US Environmental Protection Agency's Disinfectants/Disinfection by-products (D/DBPs) rule with a maximum aggregate contaminant level of 60 μg/l. The World Health Organization has been more specific by setting individual limits for DCAA (50 μg/l) and TCAA (100 μg/l).
Unfortunately, chlorine remains an important disinfectant worldwide, as it provides residual disinfection capability within water supplies. As a consequence, the use of chlorine to disinfect water is considered to some extent a necessary evil, and it is important to monitor the presence of HAAs as a DPB, and to correct excessive HAA presence as part of the water distribution process.
Various techniques exist to determine HAA presence in water, generally relying on gas-chromatography, liquid chromatography, ion-chromatography, capillary electrophoresis, electrospray ionization or similar analytical techniques. However, without pre-concentration of HAAs from bulk potable water, most of these techniques cannot reliability and reproducibly achieve required detection limits. Pre-concentration techniques, in turn, are laborious and time consuming, and often require careful process controls that generally are only obtained in a sophisticated laboratory setting. For example, EPA Method 552.2 calls for liquid-solid extraction of HAAs. A sample is adjusted to pH 5.0 and HAAs are then extracted with a preconditioned anion exchange column. Analytes are eluted with small aliquots of acidic methanol and esterified directly in this medium after the addition of methyl-tert-butyl ether (MTBE) as a co-solvent. Methyl esters of HAAs can then be quantified (i.e., as an aggregate measure of HAAs) by gas chromatography (GC) equipped with an electron capture detector (ECD) or a mass-spectrometer (MS).
Thus, in a typical testing process, water samples are typically collected in-situ using vials and then transported to an offsite laboratory for performance of these processes which is to say, these techniques often require significant cost and lead time. Most of the methods and apparatus described in the literature require expensive equipment (with substantial maintenance demands) and extensive personnel training. Also importantly, these techniques often involve direct operator contact with hazardous chemicals and involve significant latencies before problems in a water supply can be detected and corrected.
A need therefore exists for a better process and system for measuring HAAs. More particularly, a definite need exists for HAA measurement techniques which are faster and more accurate, ideally being performed in near-real time. It should be appreciate that with quick turnaround, water supplies can more quickly react to high HAA levels, so as to minimize any public exposure to these harmful substances. Further, a need exists for techniques which avoid excessive direct operator interaction with harmful substances used in the measurement of HAAs. Still more particularly, a solution to these problems could be employed remotely, e.g., with in-situ testing, and with automatic, network based monitoring, detection, correction and reporting. Ideally, such a solution would be relatively low cost, such that it could be readily employed in association with any water supply, e.g., by a local water company at many points of distribution. The present invention satisfies these needs and provides further related, advantages.